WO03011232 discloses resin-modified glass ionomer cements containing a polymer having a plurality of acidic repeating units and a plurality of polymerizable vinyl groups which can be formed in one method by partially reacting a material such as a polymeric acid anhydride with a monomer containing an acid- or acid anhydride-reactive group and containing one or more vinyl groups that will provide the desired polymerizable functionality. The acid- or acid anhydride-reactive group reacts with acid units or anhydride units in a the polymeric precursor to provide pendant vinyl groups in the resulting reaction product so that a hydrolyzable polymer is obtained. Another method involves copolymerizing anα, β-unsaturated carboxylic acid and a suitableα, β-unsaturated monomer containing one or more such pendant vinyl groups, whereby a crosslinked product cannot be avoided.
WO03061606 discloses ionomeric cements containing a polymerizable ionomer which is obtainable based on three carboxylic acid monomers, two of which are acrylic acid and itaconic acid, and the third monomer is an acryloyl- or methacryloyl derivative of an amino acid, whereby polymerizable pendant groups are not linked to the backbone by hydrolysis-stable linking groups.
Dental restorative materials are known for restoring the function, morphology and integrity of dental structures damaged by physical damage or caries-related decay of enamel and/or dentin. Dental restorative materials can be divided into two classes, indirect restorative materials and direct restorative materials.
Indirect restorations such as inlays, onlays, crowns or bridges are adhered to the damaged residual hard dental tissue with a specific dental composition, such as a dental resin cement. Adequate adhesion of the restoration typically requires the application of a primer as a pre-treatment step.
Direct restorative materials, such as dental composites are applied directly onto the dental surface and subsequently cured in situ. However, direct restorations often require pre-treatment with an adhesive or primer to enhance adhesive strength.
Common to all dental restorations is that they require high biocompatibility, resistance to the severe conditions present in the oral cavity, particularly over a longer period of time.
Glass ionomer cements (GIC), which are cured by an acid-base reaction between silicate glass powder and a polyalkenoic acid, provide high biocompatibility, good direct adhesion to the dental hard tissues and cariostatic properties through the release of fluoride ions and are widely used as direct dental restorative materials.
However, conventional glass ionomer cements are relatively brittle due to low flexural strength properties. The resistance of glass ionomer cements to mechanical stress may be improved by the choice of the polymer for a glass ionomer cement. For example, a polymer for a glass ionomer cement, which has polymerizable moieties as pendant groups can be crosslinked to increase the mechanical resistance of the resulting glass ionomer cement.
Moreover, for the purpose of the cement reaction as well as for providing adhesive properties of the dental composition to hard dental tissue, acidic groups in the polymer are required. However, acidic groups accelerate hydrolysis of pendant functional groups linked to the polymer backbone by hydrolysable groups such as ester groups. Thus, a polymer to be used in a dental composition desirably has a plurality of carboxylic acid groups and at the same time a high stability with regard to hydrolysis in order to avoid degradation of the composition during storage or when applied to hard dental tissue.
Japanese Patent Publication No. 2005-65902A discloses a dental adhesive composition comprising, as a polymerizable monomer containing a particular carboxylic acid, a carboxylic acid compound having a (meth)acryloyl group and a carboxyl group which are bound to an aromatic group. However, such a polymerizable monomer having an ester group quickly degrades in an acidic medium.
Chen et al. and Nesterova et al. (Chen et al., J. Appl. Polym. Sci., 109 (2008) 2802-2807; Nesterova et al., Russian Journal of Applied Chemistry, 82 (2009) 618-621) disclose copolymers of N-vinylformamide with acrylic acid and/or methacrylic acid, respectively. However, none of these documents mentions the introduction of a further polymerizable moiety into the copolymer.
WO2003/011232 discloses water-based medical and dental cements that can be post-polymerized after the cement reaction. The dental cements consist of two separate polymers, wherein one of the polymers has a pendant post-polymerizable moiety linked to the polymer through an ester bond. However, this ester bond between the polymer and the polymerizable moieties is again prone to hydrolytic cleavage in acidic media. Moreover, crosslinking of the glass ionomer may lead to the shrinkage of the dental composition in particular when the molecular weight of the crosslinking polymer is low.